Technical Field
The present disclosure relates to a rectangular insulated wire obtained by covering a metal conductor with a resin, and particularly relates to an insulated wire used as a coil of an electric generator installed in, for example, electric power-driven vehicles.
Background Art
Conventionally, a round wire or a rectangular wire is employed as an insulated wire (magnet wire) used for a stator of an electric generator (motor generator) installed in automobiles. By employing a rectangular wire, a fill factor of the stator can be increased as compared to a case where a conductor having a generally round cross section is employed, and thus an electric generator having a reduced size and a higher power can be obtained. Recently, along with electric generators having a reduced size and higher power as described above, an insulated wire of the electric generator for vehicles is required to have properties, such as an insulating property, resistance to thermal softening, flexibility, and a long-term heat resistance, which are improved as compared to those of a conventional configuration.
In view of improving an insulating property, a so-called enameled wire having a rectangular conductor and an insulating layer of a thermosetting resin such as polyamide-imide (PAI) formed thereon is often used as a stator coil. However, an enamel coating alone does not provide sufficient reliability to high voltage. Accordingly, in order to improve the reliability to high voltage, attempts have been made to form another insulating layer on an outside of the enameled wire.
For example, an insulated wire exists which includes, on an outside of the enamel wire, another resin layer formed of a resin such as polyimide (PI) that has a higher tensile elongation as compared to PAI (see Japanese Laid-Open Patent Publication No. 2007-149562). With such an insulated wire, it is possible to suppress an occurrence of cracks in an insulation coating due to deformation upon forming an electric coil.
Further, an insulated wire exists which includes an adhesion layer formed on an electric conductor and composed of PAI or the like and a partial discharge resistance layer formed outwardly of the adhesive layer, wherein a rate of decrease of an adhesion strength between the adhesion layer and the conductor while being elongated with respect to an adhesion strength between the adhesion layer and the conductor without elongation is less than 25% (see Japanese Laid-Open Patent Publication No. 2012-204270). With this insulated wire, an occurrence of loose coating is suppressed by reducing a decrease in an adhesion strength between the conductor and the adhesion layer, and the lowering of a partial discharge resistance can be prevented.
As a rectangular insulated wire, an insulated wire exists which includes an insulation coating that covers an outer periphery of a rectangular conductor, and the insulation coating is composed of a polyimide (PI) resin and has an elongation at break of greater than 80% (see Japanese Laid-Open Patent Publication No. 2013-191356). With this insulated wire, since the PI resin layer stretches during a bend process, occurrence of damages such as cracks in the insulation coating can be suppressed.
Further, as another rectangular insulated wire, an insulated wire exists which includes a first layer composed of PAI containing an adhesion improver, a second layer composed of PAI obtained by reaction between an isocyanate component containing 2,4′-diphenylmethane diisocyanate and dimer acid diisocyanate by a total of 10 to 70 mol % and an acid component, and a third layer composed of PI, in this order (see Japanese Laid-Open Patent Publication No. 2014-22290). With such rectangular insulated wire, an adhesion strength between the conductor and the insulation coating is 43 to 64 g/mm, and it is possible to have an improved resistance to work, and also to achieve an improved heat resistance and thermal degradation.
However, the aforementioned conventional techniques may require a severe bending process on an insulated wire, and thus, even if an insulating layer includes an upper layer having increased extensibility, there is a concern that when a minute crack occurs in the upper layer, the crack may progress and reach an outer surface of a conductor. Alternatively, even if an insulating layer is made to have an increased adhesion between an upper layer and a lower layer thereof, since an adhesion strength between the two layers is unnecessarily high, a crack from the insulating layer and reaching an external surface of the conductor may be produced when an insulated wire is bent. Therefore, none of the aforementioned techniques are sufficient in flex resistance reliability. Further, recently, vehicle power generators that generate a high voltage are rapidly spreading, and insulated wires used for such a purpose require a high partial discharge inception voltage (PDIV). However, with the aforementioned conventional techniques, the partial discharge inception voltage is not sufficient.
It is an object of the present disclosure to provide a rectangular insulated wire having improved flex resistance reliability by preventing the generation of a crack reaching the conductor while maintaining flexibility and resistance to thermal softening, and further achieves a high insulation property by having a high partial discharge inception voltage, as well as a coil and an electrical and electronic device.
The present inventors carried out assiduous studies to attain the above object, and as a result, reached the findings that, by forming a plurality of baked-coating resin layers on a conductor, the plurality of baked-coating resin layers being formed of two or more materials, and further by specifying the range of relative permittivity of at least one of the aforementioned plurality of baked-coating resin layers, flex resistance reliability can be improved since a crack reaching the conductor is prevented, and further, a high partial discharge inception voltage can be achieved, while maintaining conventional properties. The present disclosure was contrived based on the above-mentioned findings.
According to a first aspect of the present disclosure, a rectangular insulated wire includes: a rectangular conductor having a generally rectangular cross section; and a plurality of baked-coating resin layers disposed to cover the rectangular conductor, each of the plurality of baked-coating resin layers being formed of at least one resin selected from a group comprising a polyester-based resin including a trihydric or tetrahydric alcohol constituent, a polyester imide resin, a polyamide-imide resin and a polyimide resin, an adhesion strength between the plurality of baked-coating resin layers being greater than or equal to 5 g/mm and less than or equal to 10 g/mm.
According to a second aspect of the present disclosure, a coil is provided wherein the aforementioned rectangular insulated wire is wound.
According to a third aspect of the present disclosure, an electric or electronic device includes the aforementioned coil.
According to the rectangular insulated wire of the present disclosure, each of a plurality of baked-coating resin layers is formed of at least one resin selected from a group comprising a polyester-based resin including a trihydric or tetrahydric alcohol constituent, a polyester imide resin, a polyamide-imide resin and a polyimide resin. According to such a configuration, flex resistance reliability can be improved by preventing the generation of a crack reaching the conductor while maintaining flexibility and resistance to thermal softening, and further a high insulation property can be achieved by having a high partial discharge inception voltage.
Particularly, since each of the plurality of baked-coating resin layers is formed of at least one resin selected from a group comprising a polyester-based resin including a trihydric or tetrahydric alcohol constituent, a polyester imide resin, a polyamide-imide resin and a polyimide resin, even if a crack occurs in an outer baked-coating resin layer of the at least one baked-coating resin layers in a severe bending process, it is possible to prevent an occurrence of a crack in an inner baked-coating resin layer by causing a peel to occur between the two baked-coating resin layers that are adhered with an adhesion strength between coating layers of greater than or equal to 10 g/mm and less than or equal to 5 g/mm. Therefore, generation of a crack reaching the conductor can be positively prevented. The measurement of adhesion strength was carried out by making two parallel slits in a rectangular insulated wire along a longitudinal direction thereof and extending over a length of ⅓ to ½ of the long side and measuring a force applied when peeling between the slits, and the measured value was converted into a numerical value per 1 mm to obtain an adhesion strength.
Also, since an inner most layer among the plurality of baked-coating resin layers has a thickness of greater than or equal to 20 μm and less than or equal to 60 μm, a higher dielectric breakdown voltage can be obtained.
Also, since a content of trihydric or tetrahydric alcohol constituents is 30 to 90 mol % to a total number of moles of alcohol constituents in the polyester-based resin, adhesion with the conductor can be improved without affecting electrical characteristics, and occurrence of a crack reaching the conductor can be positively prevented.
Further, since the rectangular insulated wire further includes an extruded covering layer disposed over an outermost layer of the plurality of baked-coating resin layer, the extruded covering layer being formed of a thermoplastic resin, flex resistance reliability can be improved while maintaining flexibility and resistance to thermal softening, and in addition, a higher partial discharge inception voltage can be achieved.
Also, with the rectangular insulated wire of the present disclosure being wound into a coil, even in a case where a high voltage is applied, a partial discharge generation can be suppressed, and a rectangular insulated wire that can significantly suppress an occurrence of dielectric breakdown can be obtained. Particularly, a further significant effect can be obtained by applying the rectangular insulated wire of the present disclosure to an electrical and electronic devices such as motor-generators.